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MG MGA - Generator Questions

A couple questions on rebuilding my generator...

I need a new armature for my generator. I see that Moss lists them at around $47 USD which seems like a deal. Does anyone have experience with the Moss parts? I would rather use factory parts but I doubt I will ever find such a thing in new condition.

I also have a broken wire between the two field windings. Can I just solder it back on? Is there a trick to it or do I just look for any metal to metal contact?

Last question, how would one go about replacing the rear bushing? It seems to be pressed into a hole with no rear access.

Thanks for any replies!
Steve Simmons

Steve - The armature for a MGB generator will work fine in the MGA generator (they are the same generator, just a slightly greater current capacity for the MGB). Just soldering the wires together for the field coils will work fine. I don't know how much expertise you have with soldering, but all you need to do is to clean the varnish off of the ends of the two wires and then use some 400 grit sand paper to get the ends nice and shiny, tin them with solder, twist them together and solder. Just make sure that the wires get hot enough to get the solder to flow well. Put a piece of shrink sleeving on the wires before connecting them together, then slip it over the solder joint and shrink it in place so it doesn't short against the through bolt. You might want to take the armature in to an auto electric shop and have them test it and if it tests good, have them turn the commutator so it can be reused. Unless it has been subject to over current or mechanical damage, if the commutator has enough metal that it can be turned smooth and round, the armature can be reused. While you are at the auto electric shop, get a front bearing from them and they can probably supply the rear bushing also. To remove the rear bushing, use a dermal tool to cut grooves down the length of the bushing (or just pound a screwdriver down the length of the bushing) and take it out in pieces. Before installing the new bushing, it needs to be soaked overnight in light engine oil. A quick way to accomplish the soak is to place one open end of the bushing on you thumb, fill it to brimming with oil, place your other thumb over the open end (it helps to be double jointed to accomplish this), then press your two thumbs toward each other. In seconds you will see the oil ooze through the bushing and you will have completed an overnight soak in minutes. Finally, see my article on fan belt tension at: http://www.omgtr.ca/technical/tdtf_fan_belt/loosen_up.htm and heed it. A tight fan belt will destroy your generator faster than anything else. Good luck - Dave
David DuBois

To extract the bronze bushing, run a thread tap into it and pull it out.
Barney Gaylord

Thanks for the advise. While I am no expert in soldering, I do have average abilities. The wire between the two sides looks to be bare. Should it have insulation on it? Maybe it burned off and that's why it broke?

I don't have a spare MGB armature either so I have to buy one, which is why I was wondering about the Moss replacement parts. Or is it better to find a used factory part than to pay the $48 for a new repro?

And I did learn the hard way about fan belt tension about 15 years ago when I had to have my MGB generator rebuilt due to a loud rattle!

Thanks for all the great info!
Steve Simmons

Steve - The wire used for the field coils (and for the armature) is just coated with a tough varnish and looks like there is nothing on the wire. Try cleaning the ends of the wire with 400 grit sand paper, if it doesn't imediately (as in one or two passses) shine up like bright new copper, then you will have to use a sharp knife to scrape the varnish off, then sand the wire. To get a good solder joint, you have to start with bright, shiny copper. I would doubt that the armature needs to be replaced unless it has been seriously abused. If it does need replacement, it looks like Victoria British has the armatures for about $10 less than Moss. I don't think that factory original vs reproduction has much affect in the area of armatures, the ones on the market today should work fine. Cheers - Dave
David DuBois

Bought one of Moss's new generators several years ago, so far no problems. for $40 over the cost of an armature you get a complete new unit.
John H

The threads on the end of the armature are trashed. It's unfortunate because it is otherwise in good order.

I've heard that the Moss generators are far-east products that are inferior to the original units. That's my real concern, but it's good to hear that the rumors may not be entirely true. Still, I would rather rebuild the original even if it's only the shell and end plates that are left!
Steve Simmons

Hi, Steve - the size of the nut on the end of the armature is relatively unimportant, so if the slot where the Woodruff key lives is OK, there's no reason the armature can't be re-threaded to a smaller size, even metric if you want. The only purpose of the nut is to hold the pulley and fan on the shaft, and there's little axial load on that part, anyway, if the belt lines up. A flat washer, lock washer, and maybe some threadlocker, and you're golden.

The "proper" way to do this is to turn the armature down to the next smaller size on a lathe, but there's no reason you couldn't do this freehand with a file and then re-thread the "stub" (thread the stub with the die the correct way first, then turn the die over to get the threads all the way up to the shoulder). After all, you're planning to trash the armature anyway, right.

Barney is correct about using a tap to get the bush out, but you often have to break it up, regardless. I've used an icepick driven alongside the bushing with good results.

Best of luck, and please let us know how you make out - - Alec
Alec Darnall

That's a really good point about rethreading the armature. I'll try it tonight!
Steve Simmons

Steve,
Regarding the varnish on the windings, I have used Indian Head Gasket Shellac on generator windings and had great success. The varnish will coat any bare places and harden up to a nice coating. I recommend this over the heat shrink only because the heat shrink usually shrinks where you don't want it to, and you have to work some to get it where it was supposed to go.
mike parker

And the point of the varnish / shellac is to prevent corrosion? Or short circuit? Or both?
Steve Simmons

Steve - Mike has a valid point - the shellac prevents movement, and it's the movement that can cause the coating on the wires to rub off and thus cause a short circuit (more an issue on the field coild than on the armature - it's usually well coated already). If you opt for Indian Head, make sure it's the hard-setting variety. Their line of "Aviation" gasket sealers are particularly good if you don't ever plan on removing the part you use it on.

The wire connecting the two field coils can be left in the open, or you can use a short piece of wiring "spaghetti" or heat-shrink if you want to. Don't use tape, as it will eventually unroll in the airstream that goes through the case.

Best wishes - - Alec
Alec Darnall

Tonight I took a die grinder to the old threads, or what was left of them. Took it down until the old thread disappeared, still a bit too large so I went a tiny bit more. Too far, oops! But it was close so I ran a 3/8"-16 die over the shaft and have a nice shiney new set of threads. So far so good....
Steve Simmons

Snag. The material around the field coils is coming apart. Is there an easy way to repair this problem?

I also need to replace the two wires going from the field coils to the F terminal because the insulation is breaking off in dried-out chips.

I'm starting to feel this is getting beyond my means to refurbish. Basically the only pieces that are still good are the steel housing and aluminum end plates.
Steve Simmons

Steve - you know the trick about using a short piece of rope to hold the pulley still while you tighten the nut, don't you? If not, get a three or four foot long piece if natural fiber rope (hemp or sisal) and tie one end to a fixed point on the car (or on the vise if you've got it out of the car) then wrap it two or three times around the pulley. It'll hold the pulley still while you tighten the nut better than anything else I've ever tried. If it wants to slip, just dampen the rope a bit, and it'll lock right on.

Congrats on the new threads - hope it works out for you - - Alec
Alec Darnall

Oops - we posted at almost the same time. The only sure cure is to re-wrap the field coils with cloth friction tape, and that requires removing the screws in the side of the generator, and taking the field coils out. Then, when you wrap the coils with a 50% coverage wrap (each successive round of tape covers 50% of the previous layer), you should make sure that the loose end is captured under the coil when you screw the field pole piece back into place.

The only reliable tool to remove those screws that I have found in the typical home shop is the manual impact tool that you fit a bit into, turn slightly, then hit with a BFH. The professional shops use a large "wheel" screwdriver to accomplish the same thing.

If you don't want to re-wrap, the previous idea about using gasket sealer has some merit. You might have to apply several coats to get it stiff enough to satisfy yourself, but once it hardens, you should be all right. When you're done, just think about the stories you can tell - - -

But, you're right - this is getting way past the point that most enthusiasts would be willing to go - - Alec

Alec Darnall

An impact driver is exactly what I used to remove those screws earlier this evening. One of them almost didn't come out at all. I gave up twice before finally getting it loose. Amazing! Maybe I'll keep at it for now. I like the friction tape idea.
Steve Simmons

More photos here, taken by a Mini owner:

http://s44.photobucket.com/albums/f36/inim_mini/Memorial%20Day%20British%20Run/
Steve Simmons

Sorry, posted in wrong thread. I'm an idiot. :(
Steve Simmons

Steve,

Another type of tape for insulating the field windings is Scotch 27 Glass Cloth Electrical Tape. I use the narrow 1/2" width for the ease of working with it. Stable up to 266¼ F. Available from Waytek Inc. Part #21013 www.waytekwire.com

Why did the original generator fail?

-M.S.
Martin Straka

I have no idea why it failed, but the wiring inside appears quite old. It may not have ever been rebuilt, even when the car was restored a few years ago.

At around the same time that it stopped charging, the front bearing started making a racket. Upon inspection I found the belt a bit too tight as set by the previous owner. Yes, I've owned the car for over three years and have never adjusted the fan belt! I'm just suprised I never noticed it.
Steve Simmons

Steve,
Be cautious when installing the new generator you've rebuilt. Make certain that the problem for the failure is corrected, certain that a faulty regulator or some other electrical fault didn't ruin the generator the first time. It sounds like the front bearing was the culprit. You don't want to have to do the repairs a second time. Check the charging system to the factory specs before driving away, or at least make certain that the new generator isn't getting excessivley hot during the first few minutes of operation. -M.S.
Martin Straka

Steve
I have three original,used generators which I will sell cheap plus shipping. i did the Moss alt conversion.. I'm in NY. Also FYI listers, I havean mga 1500/1600 head,no cracks,two cranks, one uncut,one needs welding on #1 journal. Thanks.
John
s john

This thread was discussed between 31/05/2006 and 09/06/2006

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